ABSTRACT Chronic kidney disease (CKD) is a devastating renal condition that leads to kidney failure and causes other systemic complications. It is estimated that CKD affects more than 25 million people in the US and its incidence in the population is growing. While various etiologies underlie CKD, including diabetes, acute kidney injury, genetic and environmental factors, the mechanisms that contribute to the progression of CKD are less understood. Accumulating evidence suggests that recurrent injury by uremic toxins and other stress mediators leads to genomic instability and cell cycle abnormalities in CKD patients. Although, damage to the genetic material, if unrepaired, is detrimental to the tubular cell, since it interferes with DNA replication and tubular regeneration, the role of DNA damage response in regulating renal tubular repair and cellular senescence programs has not been established. Recently, we identified mutations in a Fanconi anemia-associated DNA repair enzyme, FAN1, as causing CKD in affected individuals. FAN1 has functions in DNA replication and regulates DNA cross-link repair. However, its role in preventing CKD is not understood. To study Fan1 role in the kidney we generated a Fan1-null mouse that recapitulates the human FAN1-deficient CKD phenotype. We now demonstrate that Fan1-null kidneys display increased sensitivity to genotoxic and non-genotoxic tubular injury, whose defective repair activates renal tubular senescence and fibrogenic programs. Based on our preliminary results, we hypothesize that impaired DNA damage response in the renal tubular cells leads to defective tubular repair and underlies the pathogenesis of chronic kidney disease. In Specific Aim 1, we will investigate the role of Fan1 in renal tubular cell senescence after cisplatin- and unilateral ureteral obstruction injury (UUO), using a variety of immunohistochemical and molecular approaches on the newly generated Fan1-null mouse model. Recent studies in our lab indicate that loss of Fan1 affects cell cycle checkpoint activation and causes mitotic abnormalities in kidney tubular cells. Based on these observations Specific Aim 2 will address the role of Fan1 in mitotic regulation and will examine the efficacy of therapeutic strategies designed to modulate cell cycle progression in Fan1-null kidneys. In Specific Aim 3, we will characterize the functional interaction between FAN1 and a pediatric CKD gene, SDCCAG8, in the kidney. We will also use the BioID proximity labeling method to identify proteins that are associated with Fan1 in the cell, in order to gain insights into its functional pathways. In summary, the Fan1-mouse model provides us with a novel opportunity to examine the molecular pathways associated with the development of chronic kidney disease, as well as to assess the role of DNA damage response pathway in the progression of this human disease in hopes of developing new treatments. !